By way of non-limiting example, “weak signals” are signals for which:
the signal/noise ratio is low and/or
the amplitude or the intensity is low and/or
the information contained is fragmented and/or
the information contained is composed of micro-events in coincidence or in occurrence.
This method is designed to assist the actors from the industrial and medical world, from security and from defense, to control the processes of identification in a reliable manner for the management of performances and of risks.
Synthetically reconstructing an object illuminated by a laser over a wide range of wavelengths is a problem that covers a broad spectrum of theoretical and industrial applications in: the field of security and of defense (for example the identification of an IED—acronym for “Improvised Explosive Device”) or the field of civilian transport (for example the identification of a pedestrian or a vehicle in the field of transport safety) or the medical field (for example the tomographic identification of cancerous cells in a tissue).
However robust the detection systems employed, the information supplied in these very noisy environments requires innovative data and knowledge processing methods enabling the object to be localized and synthetically reconstructed without loss of spatial resolution and it to be identified in a reliable manner.
Numerous scientific, technical and industrial studies have been undertaken in the field of inversion problems; the results obtained remain unsatisfactory due to their high sensitivity to the variations in the measurement parameters coming from weak signals, from the environment and from the instability of the system as a whole. The development of methods for inversion processing and reliable reconstruction allowing a resolution compatible with the systems used remains a major problem for the industry.
By way of non-limiting example, the difficulties encountered in the conventional methods of three-dimensional reconstruction starting from objects illuminated by an electromagnetic wave or excited by an elastic wave have as sources:
the propagation noise,
the instability of the sensor with respect to the objects,
the noise of the sensor and of the associated electronics,
the high spatial and time resolution imposed,
the unknown structure of the total noise,
the need for correlating in real time,
the variation in real time of the information,
the non-linear problem associated with the inversion,
the high non-linearity of the behavior of the signal.